Plasma treatment system

ABSTRACT

A plasma treatment system for treating a workpiece with a downstream-type plasma. The processing chamber of the plasma treatment system includes a chamber lid having a plasma cavity disposed generally between a powered electrode and a grounded plate, a processing space separated from the plasma cavity by the grounded plate, and a substrate support in the processing space for holding the workpiece. A direct plasma is generated in the plasma cavity. The grounded plate is adapted with openings that remove electrons and ions from the plasma admitted from the plasma cavity into the processing space to provide a downstream-type plasma of free radicals. The openings may also eliminate line-of-sight paths for light between the plasma cavity and processing space. In another aspect, the volume of the processing chamber may be adjusted by removing or inserting at least one removable sidewall section from the chamber lid.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. ProvisionalApplication No. 60/374,010, filed Apr. 19, 2002, the disclosure of whichis hereby incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

[0002] The present invention relates generally to plasma processing, andmore particularly to a plasma treatment system configured to performdownstream-type plasma treatments.

BACKGROUND OF THE INVENTION

[0003] Plasma treatment is commonly applied for modifying the surfaceproperties of workpieces used in applications relating to integratedcircuits, electronic packages, and printed circuit boards. Plasmatreatment systems are configured to produce a direct plasma from aprocess gas and expose a surface of a substrate or workpiece withgenerated active species from the direct plasma to remove surface atomsby physical sputtering, chemically-assisted sputtering, or chemicalreactions. The physical or chemical action may be used to condition thesurface to improve properties such as adhesion, to selectively remove anextraneous surface layer of a process material, or to clean undesiredcontaminants from the surface. Plasma treatment is used in electronicspackaging, for example, to increase surface activation and/or surfacecleanliness for eliminating delamination and bond failures, improvingwire bond strength, ensuring void free underfill, removing oxides,enhancing die attach, and improving adhesion for encapsulation.

[0004] Plasma treatment systems may be integrated into in-line andcluster systems or batch processes in which groups of workpieces areprocessed by successive plasma exposures or processing cycles.Workpieces may be supplied by various methods, include delivery in amagazine, individual delivery by a conveyer transport system, or manualinsertion into the process chamber. Plasma treatment systems may also beprovided with automated robotic manipulators that coordinate workpieceexchange into and out of the process chamber for plasma processingoperations.

[0005] Conventional plasma treatment systems have failed to provideadequate process uniformity across the surface of individual workpieces.The plasma density must be precisely and accurately controlled at allpositions on the surface of the workpiece so that it is substantiallyuniform across the surface. Critical parameters for controlling theuniformity of the plasma include the spatial uniformity of theexcitation power and the dispersion of the process gas. A non-uniformplasma density at the surface of the workpiece degrades processreliability and reduces the process yield. To achieveworkpiece-to-workpiece uniformity, the process gas must be evenlydispersed and uniformly ionized by the excitation power so that the fluxof active species is spatially uniform across the surface of theworkpiece.

[0006] Conventional plasma treatment systems have likewise failed toachieve adequate reproducibility of the plasma treatment betweensuccessive batches of workpieces. Batch-to-batch reproducibility dependson the precise control of process variables and parameters so thatsuccessive workpieces are exposed to substantially identical plasmaconditions. Moreover, conventional plasma treatment systems areincapable of rapidly processing workpieces with a throughput amenable toautomated process lines or fabrication requirements. System throughputand uniformity of the plasma treatment must be maximized for reducingproduction costs.

[0007] Conventional in-line plasma treatment systems also lack theability to generate a downstream-type plasma that is substantially freeof ions, electrons and light in at least the visible region of theelectromagnetic spectrum. As is well-known, a direct plasma is acombination of multiple different species including ions and electronsthat have a net charge and source gas molecules and free radicals thatare neutral. Free radicals are gas molecules that are nearly ionized yetretain their full complement of electrons so they are neither positivelynor negatively charged. Workpieces may be processed with a direct plasmacontaining all plasma species or with a downstream-type plasma includingprimarily free radicals. Processing workpieces with a direct plasmapromotes treatment with both physical action due to ion and electronbombardment and chemical action arising from surface interaction of thefree radicals. On the other hand, processing with the downstream-typeplasma involves primarily chemical action.

[0008] Conventional plasma treatment systems generally include a fixeddimension plasma chamber and a substrate support in the plasma chamberthat holds the workpiece at a fixed position between opposed treatmentelectrodes. Because the workpiece is located at a fixed position, thesurface to be plasma treated is likewise spaced relative to thetreatment electrodes. The fixed position is chosen to provide a spacingeffective to provide an effective plasma treatment for workpieces of agiven thickness. It follows that, as the thickness of the workpiecebeing treated in the system changes, the location of the surface is nolonger at the desired fixed position so that the efficiency of theplasma treatment may be reduced. Therefore, conventional plasmatreatment systems are ill equipped to accommodate changes in workpiecethickness.

[0009] There is thus a need for an in-line plasma treatment system thatcan provide a downstream-type plasma for treating workpieces in theplasma chamber and that can accommodate workpieces of differingthickness while maintaining an effective treatment efficiency.

SUMMARY

[0010] The present invention addresses these and other problemsassociated with the prior art by providing a plasma treatment systemcapable of performing a downstream-type plasma treatment. The plasmatreatment system includes a vacuum chamber including a processing space,a chamber lid, and a plasma cavity defined in the chamber lid, aworkpiece holder positioned in the processing space, a vacuum sourcecoupled in fluid communication with the vacuum chamber, a process gassupply coupled in fluid communication with the vacuum chamber, and afirst plasma excitation source. The plasma cavity and processing spaceare in fluid communication. The process gas supply is capable ofproviding process gas to at least the plasma cavity, the vacuum sourceis capable of evacuating the processing space and the plasma cavity, andthe first plasma excitation source is operable for exciting process gasin the plasma cavity to generate a plasma. The plasma excitation sourcefurther includes a grounded plate positioned between the plasma cavityand the processing space. The grounded plate includes a plurality ofopenings capable of prohibiting or, at the least, substantially reducingthe transfer of charged species, such as ions and electrons, from theplasma cavity to the processing space. However, the openingspreferentially allow the transfer of free radicals from the plasmacavity to the processing space. According to this aspect of theinvention, a downstream-type plasma free, or substantially free, ofcharged particles and photons can be generated at the workpiece forperforming plasma treatments by the chemical action of the radicalswithout the physical action otherwise provided by the charged particles.

[0011] According to the principles of the invention, a method isprovided for treating a workpiece with a plasma. The method includesplacing the workpiece in a processing space of a plasma processingsystem, generating a direct plasma comprising charged species and freeradicals, filtering charged species from the direct plasma to create adownstream-type plasma including free radicals, and exposing theworkpiece in the processing space to the free radicals in thedownstream-type plasma.

[0012] According to another aspect of the invention, a plasma treatmentsystem includes a vacuum chamber having a chamber base and a chamber lidmovable relative to the chamber base between a closed position thatdefines a processing space and an open position for transferring aworkpiece into and out of the processing space, a vacuum source coupledin fluid communication with the vacuum chamber, a workpiece holderlocated in the processing space, a process gas supply in fluidcommunication with the vacuum chamber, and a plasma excitation source.The process gas supply is capable of providing process gas to theprocessing space, the vacuum source is capable of evacuating theprocessing space, and the plasma excitation source is operable toprovide a plasma in the processing space generated from the process gas.The chamber lid further includes a first sidewall section capable ofbeing removed from the chamber lid for changing a vertical dimension ofthe vacuum chamber. According to this aspect of the invention, thevertical dimension of the chamber may be varied to accommodateworkpieces of differing thickness by compensating for substratethickness by placing the exposed surface of the workpiece at apredictable distance from the treatment electrode.

[0013] According to the principles of the invention, a method isprovided for plasma treating a workpiece in a processing space of avacuum chamber having a chamber lid. The method comprises placing aworkpiece in the processing space, and varying a volume of the chamberlid to alter the distance from an exposed surface of the workpiece to atreatment electrode positioned in the chamber lid based upon a thicknessof the workpiece.

[0014] These and other objects and advantages of the present inventionshall become more apparent from the accompanying drawings anddescription thereof.

BRIEF DESCRIPTION OF THE FIGURES

[0015] The accompanying drawings, which are incorporated in andconstitute a part of this specification, illustrate embodiments of theinvention and, together with a general description of the inventiongiven above, and the detailed description given below, serve to explainthe principles of the invention.

[0016]FIG. 1 is a perspective view of a plasma treatment system inaccordance with the principles of the present invention;

[0017]FIG. 2A is a side schematic and partially broken view of theplasma treatment system of FIG. 1;

[0018]FIG. 2B is a side schematic and partially broken view of theplasma treatment system of FIG. 1 in which the chamber lid is in aclosed position;

[0019]FIG. 2C is a detailed side view of the plasma treatment system ofFIG. 1;

[0020]FIG. 3 is a front view of the plasma treatment system of FIG. 1;

[0021]FIG. 4 is a schematic block diagram illustrating a control systemfor the plasma treatment system of FIG. 1;

[0022]FIG. 5 is a flow chart illustrating a process of implementing aplasma processing cycle utilizing the control system of FIG. 4;

[0023]FIG. 6 is a side view of a substrate support in accordance with analternative embodiment the principles of the present invention;

[0024]FIG. 7 is a partial front view of the substrate support of FIG. 6;

[0025]FIG. 8 is a top view of a plasma chamber in accordance with theprinciples of the invention;

[0026]FIG. 9 is a sectional view taken generally along line 9-9 of FIG.8;

[0027]FIG. 10 is a sectional view taken generally along line 10-10 ofFIG. 9;

[0028]FIG. 11 is a detailed view of a portion of FIG. 10;

[0029]FIG. 12 is an exploded view of the plasma chamber of FIGS. 8-11;

[0030]FIG. 13 is a perspective view of an alternative embodiment of agrounded plate for use with the plasma chamber of FIGS. 8-12;

[0031]FIG. 14 is a perspective view of an alternative embodiment of agrounded plate for use with the plasma chamber of FIGS. 8-12;

[0032]FIG. 15 is a sectional view similar to FIG. 9 of an alternativeembodiment of a plasma chamber in accordance with the principles of theinvention;

[0033]FIG. 15A a detailed view of a portion of FIG. 15;

[0034]FIG. 16 is a sectional view similar to FIG. 10 of the, plasmachamber of FIG. 15;

[0035]FIG. 17 is a detailed view of a portion of FIG. 16; and

[0036]FIG. 18 is an exploded view of the plasma chamber of FIGS. 15-17.

DETAILED DESCRIPTION OF THE INVENTION

[0037] The present invention, in accordance with the principles andobjectives herein, provides an apparatus and a method for processing aworkpiece with a plasma. The present invention provides a plasmatreatment system configured to provide a uniformly dense plasma, rapidpump-down and venting cycles, reproducible processing conditions, andsimplified material handling. The system advantageously requires areduced excitation power to initiate and sustain a uniformly denseplasma in the processing space, while employing a control algorithm thatminimizes the cycle time required to process each successive workpiece.

[0038] A plasma treatment system 10, in accordance with the principlesof the present invention, is illustrated in FIGS. 1, 2A-2C and 3.Referring to FIG. 1, plasma treatment system 10 includes a processingchamber 12, a loading station 20, and an exit station 22, which aresituated on a substantially flat and mechanically stable surface 24 atopan instrument cabinet 26. Processing chamber 12 includes a chamber lid14 hingeably connected to a chamber base 18 by a hinge assembly 16.Chamber lid 14 is selectively positionable between an open position, asshown in FIGS. 1 and 2A, and a closed position, as shown in FIG. 2B.Chamber base 18 and chamber lid 14 are preferably formed of anelectrically conductive material suitable for high-vacuum applications,such as an aluminum alloy or a stainless steel.

[0039] Chamber lid 14 includes a domed ceiling 28 and an integralsidewall 30 encircled by a flat rim 32. A viewport opening 38 isprovided in ceiling 28 for holding a viewport 34. As best shown in FIG.2C, viewport 34 is a substantially planar panel attached to chamber lid14 by a frame 35 and fasteners 36. An O-ring 40 is received within agroove 42 that circumscribes viewport opening 38. Viewport 34compressively engages O-ring 40 to create a vacuum-tight seal, where thesealing force is supplied collectively by the pressure differentialbetween the interior and exterior of processing chamber 12 and byfasteners 36. Viewport 34 is constructed of a dielectric ceramic, suchas quartz, that has a low sputtering coefficient, is gas impermeable,and has a wide transmission range for optical wavelengths. O-ring 40 ispreferably formed of an elastomer such as Viton®.

[0040] Chamber base 18 includes a floor wall 44 integral with a sidewall46 which is encircled by a flat lip 48. Lip 48 includes acircumferential groove 50 for receiving a conductive resilient sealingmember or O-ring 51 that provides an electrically-conductive pathway anda substantially vacuum-tight seal between chamber lid 14 and chamberbase 18. The dimensions of groove 50 and O-ring 51 are selected forcreating a vacuum-tight seal. It may be appreciated that O-ring groove50, and therefore O-ring 51, may be positioned in either chamber lid 14or chamber base 18 without departing from the spirit and scope of thepresent invention. It is appreciated that particulates from thesurrounding environment are less likely to attach to, and compromise thesealing ability of, O-ring 51 if positioned in chamber lid 14.

[0041] O-ring 51 is a conductive elastomer gasket, preferably formed ofa composite of a conductive fill powder impregnated in an elastomerbinder, such as a powder of silver and aluminum in silicone. Anexemplary O-ring 51 is formed of a conductive composite manufactured andmarketed under the trade name Cho-seal® by EMI Shielding Products, adivision of Parker Hannifin Corp. (Cleveland, Ohio).

[0042] In another aspect, chamber base 18 further includes a workpieceholder or substrate support 64 configured to receive and support a partor workpiece 56. Generally, workpiece 56 is a rectangular, planarstructure that includes a periphery having opposed side edges 58, 59 ofa predetermined thickness, a leading edge 60, and a trailing edge 62.Opposed side edges 58, 59 are separated by a predetermined maximumtransverse width that is measured perpendicular to a longitudinal axisof workpiece 56. Workpiece 56 may be a strip type part, such as a ballgrid array (BGA) or a metal lead frame, singulated BGA's carried in anAuer boat, or a pallet carrying multi-chip electronic modules,integrated circuit chips, or the like. Workpiece 56 may also be anydisk-shaped semiconductor wafer or substrate formed of silicon, galliumarsenide, and other semiconductor materials familiar to persons ofordinary skill in the art and may include patterned areas ofmetallization, contacts, insulating layers and the like.

[0043] As best depicted in FIG. 2C, substrate support 64 comprisesopposed side rails 66 a, 66 b that extend vertically from asubstantially planar support platform 68. Side rail 66 a is in a spacedrelationship relative to side rail 66 b along the longitudinal axis ofsupport platform 68 so that the maximum width between side edges 58 and59 of workpiece 56 may be accommodated. For convenience, side rail 66 awill be detailed below with the understanding that side rail 66 b has anidentical structure. Side rail 66 a protrudes above a horizontal planethat includes lip 48 and incorporates an elongate channel 72, as bestshown in FIG. 3, that extends parallel to a longitudinal axis ofsubstrate support 64. Channel 72 has a U-shaped cross-sectional profilethat is dimensioned to slidingly receive side edge 59 of workpiece 56therein. Opposed extremities of channel 72 include a flared lip 74, asbest shown in FIG. 3, that physically captures side edge 59 of workpiece56 during loading. By way of example and not limitation, the processingchamber 12 and the substrate support 64 may be configured to acceptworkpieces 56 having maximum dimensions of 2.7″ (wide)×9.25″ (long)×⅜″(thick) or maximum dimensions of 6″×12″×1″. In other embodiments, theprocessing chamber 12 may be configured to accept workpieces 56 havingmaximum plan dimensions of 12″ by 12″.

[0044] Referring to FIG. 1, loading station 20 and exit station 22 areproximate to respective opposed ends of processing chamber 12 and areadapted for shuttling workpieces 56, 56′ into and out of processingchamber 12. Loading station 20 includes a substantially planar supportplatform 76 and opposed loading side rails 78 a and 78. Loading siderail 78 a is in a spaced relationship relative to loading side rail 78 balong the longitudinal axis of support platform 76 so that the maximumwidth of workpiece 56 may be accommodated. For convenience, side rail 78a will be detailed below with the understanding that side rail 78 b issubstantially identical. Loading side rail 78 a protrudes above ahorizontal plane that includes lip 48 and incorporates an elongatechannel 82. Channel 82 has a U-shaped cross-sectional profile that isdimensionally adapted to slideably receive one opposed side edge 58 or59 of workpiece 56 therein. Opposed extremities of channel 82 include aflared lip 80 that physically captures the side edges 58, 59 ofworkpiece 56. Support posts 84 extend from a bottom surface of thesupport platform 76 to surface 24.

[0045] Exit station 22 is configured similarly to loading station 20.Exit station 22 includes opposed unloading side rails 86 a, 86 b thatextend upwardly and outwardly from a planar support platform 88. Forconvenience, side rail 86 a will be detailed below with theunderstanding that side rail 86 b has an identical structure. Side rail86 a protrudes above a horizontal plane that includes rim 48 andincorporates a longitudinal channel 90. Channel 90 has a U-shapedcross-sectional profile that is dimensioned to slideably receive one ofthe two peripheral edge 58′, 59′ of processed workpiece 56′ therein.Opposed extremities of channel 90 include a flared lip 91 that aids inphysically capturing the side edges 58′, 59′ of processed workpiece 56′during unloading. Support posts 92 extend from a bottom surface ofsupport platform 88 to surface 24.

[0046] Plasma treatment system 10 further includes pinch wheels 99attached to loading station 20 and exit station 22 and a positioninglever 94. Pinch wheels 99 are operable to make fine adjustments in thepositioning of workpiece 56 or workpiece 56′. Lever 94 is operable tomove along the length of a slot 96 defined in the top surface 24 ofinstrument cabinet 26 and to also translate vertically. A drivingmechanism (not shown) is attached to lever 94 and is operable to movearm 94 vertically and longitudinally in slot 96. Lever 94 is positionedentirely outside of processing chamber 12 during a plasma processingcycle.

[0047] Positioning lever 94 further includes a rod 97 having a firstfinger 98 a that selectively abuts a rear edge 62 of workpiece 56 heldbetween loading side rails 78 a,b and a second finger 98 b thatselectively abuts a rear edge 62 of second workpiece 56 held betweensides rails 66 a,b. It may be appreciated that fingers 98 a,b can beresiliently biased relative to rod 97 and, in addition, that fingers 98a,b may further include a sensor for detecting resistance in the linearmovement of positioning lever 94 due to, for example, a workpiecemisaligned with a set of side rails.

[0048] During a workpiece loading operation, workpiece 56 is deliveredby an automated conveying system (not shown) and positioned in loadingside rails 78 a,b on loading station 20. Pinch wheels 99 of loadingstation 20 are used to move the workpiece 56 short distances for properpositioning. After chamber lid 14 is opened, positioning lever 94 islowered from its initial position and linearly actuated so that finger98 a will engage rear edge 62 and push workpiece 56 along loading siderails 78 a,b toward substrate support 64. The front edge 60 of workpiece56 will traverse the gap between loading side rails 78 a,b and siderails 66 a,b. Opposed side edges 58, 59 of workpiece 56 will beslideably received by side rails 66 a,b. Thereafter, the positioninglever 94 will continue to push the workpiece 56 until it is suitably andaccurately positioned on substrate support 64. Preferably, the center ofworkpiece 56 is positioned coaxial with the central vertical axis orcenterline of the processing chamber 12. Positioning lever 94 thentranslates vertically so that finger 98 b will clear the leading edge ofworkpiece 56 as lever 94 is retracted to its initial position.

[0049] If processed workpiece 56′ resides on substrate support 64 duringthe workplace loading operation, finger 98 b engages rear edge 62′ andpositioning lever 94 sweeps the processed workpiece 56′ toward exitstation 22. Front edge 60′ of processed workpiece 56′ will cross the gapbetween the processing chamber 12 and exit station 22. Side edges 58′,59′ of processed workpiece 56′ are captured by unloading side rails 86a,b. With continued linear movement, processed workpiece 56′ iscompletely removed from processing chamber 12. Pinch wheels 99 of exitstation 22 are used to move the workpiece 56′ short distances for properpositioning in preparation for transport to the next processing station.

[0050] Hinge assembly 16 is adapted so that chamber lid 14 may beselectively pivoted relative to chamber base 18 between an openposition, as best illustrated in FIG. 2A, and a closed position, as bestillustrated in FIG. 2B. Hinge assembly 16 includes at least two brackets100, as best shown in FIG. 1, that are disposed in a spaced relationshipalong the non-vacuum side of sidewall 46. When chamber lid 14 iscantilevered into a closed position, chamber lid 14 and-chamber base 18bound a vacuum-tight processing space 102, as shown for example in FIG.2B.

[0051] Each bracket 100 includes a V-shaped brace 104 and a nub 106mounted with fasteners 108 to a non-vacuum side of sidewall 46. Eachbrace 104 is carried by a hinge pin 110 received within an aperture 112near the bend in brace 104 and within a coaxial aperture 124 in nub 106.As shown in FIG. 1, hinge pin 110 is shared by both brackets 100.Returning to FIG. 2A, one end of brace 104 is connected to thenon-vacuum side of sidewall 30 of chamber lid 14. A second end of eachbrace 104 includes an aperture 114 that receives a connecting rod 116that is also shared by both braces 104.

[0052] Connecting rod 116 is further attached to a rod end 118 that isthreadingly carried by one end of a piston rod 120 of a bi-directionalpneumatic cylinder or lid actuator 122. Rod end 118 further includes anaperture (not shown but similar to, and collinear with, aperture 114)with an inner diameter sized to slideably receive connecting rod 116therein. Piston rod 120 is adapted for reciprocating linear, verticalmotion so that brace 104 can pivot about hinge pin 110 to cantileverchamber lid 14 between an open position and a closed position. As shownin FIG. 2C, the opposed end of lid actuator 122 is affixed via amounting block 126 to a structural support (not shown) within instrumentcabinet 26.

[0053] Referring to FIG. 2B, in one aspect of the present invention, anobround bearing 128 is slidingly received within aperture 124 of nub106. Obround bearing 128 has an exterior, annular surface of an outerdiameter chosen to frictionally fit within aperture 124 and an interiorbore 130 that is dimensioned to receive hinge pin 110. Bore 130 has asubstantially oval cross-sectional profile with a vertical major axis,as viewed normal to the longitudinal axis of bore 130. When chamber lid14 is in an open position, as shown in FIG. 2B, a length of one end ofhinge pin 110 will contact a lower interior surface of bore 130. Aschamber lid 14 is pivoted by the lid actuator 122, hinge pin 110 rotatesabout a longitudinal axis thereof. During rotation, the outer surface ofhinge pin 110 remains in contact with the lower interior surface of bore130. When lip 32 contacts the surface of O-ring 51, as shown in FIG. 2B,lid actuator 122 will continue to extend so that the chamber lid 14moves downward to compress O-ring 51. Due to the presence of obroundbearing 128, hinge pin 110 is free to translate vertically upward inbore 130.

[0054] Referring to FIG. 2C, in which the chamber lid 14 resides in aclosed position, the interior peripheral surface of the chamber lid 14and chamber base 18 bounds processing space 102. The vacuum seal isenhanced by the further compression of O-ring 51 between chamber base 18and chamber lid 14. The additional compression of O-ring 51 results fromthe pressure differential between atmospheric pressure acting on theexterior of chamber lid 14 and the vacuum within processing chamber 12that applies a force that urges chamber lid 14 vertically downwardtowards chamber base 18. Hinge pin 110 translates vertically and withminimal transverse motion due to the presence of obround bearing 128.

[0055] Bore 130 within obround bearing 128 affords an additional degreeof vertical freedom for hinge pin 110, as compared with a conventionalbearing having a bore of a circular cross-sectional profile. Chamber lid14 is free to move vertically in response to the forces that compressO-ring 51. As a result, the vacuum-tight seal between lip 32 and O-ring51 is uniform about the circumference of groove 50. In a preferredembodiment, the presence of obround bearing 128 provides approximately50 mils of vertical movement for hinge pin 110.

[0056] A pressure gauge 52 is connected via tubing 53 to an openingprovided in sidewall 46. Pressure gauge 52 is operable to sense thevacuum pressure within processing space 102 and provides a pressurefeedback signal. An exemplary pressure gauge 52 is a capacitancemanometer, such as the Baratron® Capacitance Manometer manufactured byMKS Instruments (Andover, Mass.). A bleed valve 54 is connected viatubing 55 to another opening provided in sidewall 46. Bleed valve 54 isoperable to vent processing chamber 12 with ambient air or a suppliedgas, such as nitrogen.

[0057] Referring to FIG. 3, plasma treatment system 10 is connected forfluid communication with a vacuum pumping system 134 through a large,centrally located exhaust port 136 in bottom wall 44 of chamber base 18.Vacuum pumping system 134 includes a conical reducing nipple 138, avacuum valve 140, an exhaust vacuum conduit (not shown), and a vacuumpump 144.

[0058] Opposing ends of conical reducing nipple 138 carry a first vacuumflange 146 and a second vacuum flange 166. First vacuum flange 146 isconnected to exhaust port 136 via a screened centering ring 148circumscribed by O-ring 150 and a plurality of bulkhead clamps 152.Bulkhead clamps 152 are symmetrically disposed about the periphery offirst vacuum flange 146. Each bulkhead clamp 152 has a tapered segment154 that is adapted to engage a complementary lower surface of firstvacuum flange 146 and a block portion 156 that further includes bores(not shown) for removably receiving fasteners 160. Preferably, fasteners160 are threaded bolts attachable to openings having complementaryinternal threads (not shown) in bottom wall 44. To create a vacuum-tightseal, fasteners 160 are tightened to a preselected torque in a patternedsequence so as to uniformly compress O-ring 150.

[0059] Vacuum valve 140 carries an upper vacuum flange 162 connected forfluid communication via a vacuum fixture 164 with second vacuum flange166 which is carried by conical reducing nipple 138. Vacuum fixture 164comprises a removable clamshell clamp 168 with a wingnut closure 170 anda through-bore centering ring 172. When wingnut closure 170 istightened, an O-ring 174 carried by centering ring 172 is compressed tocreated a vacuum-tight seal. Vacuum valve 140 also is further connectedfor fluid communication with vacuum pump 144.

[0060] Vacuum pump 144 may comprise one or more vacuum pumps as would beapparent to one of ordinary skill in the art of vacuum technology. Apreferred vacuum pump 144 is a single rotary-vane vacuum pump of thetype manufactured by, for example, Alcatel Vacuum Technologies Inc.(Fremont, Calif.), that has a pumping rate of about eleven cubic feetper minute and which, due to the high conductance of processing chamber12, can evacuate processing space 102 to a vacuum pressure of about 200mTorr in less than about six seconds. Alternative vacuum pumps 144include dry pumps and turbomolecular pumps.

[0061] In another aspect of the present invention, a vacuum distributionbaffle 180 is positioned on a shoulder 178 on the interior of chamberbase 18. Vacuum distribution baffle 180 is a flat elongate plate 182perforated by a plurality of orifices 184. Orifices 184 restrict theflow of process gas toward the inlet of vacuum pumping system 134 so asto divert the pressure differential. As a result, the entire processedsurface of workpiece 56 will be uniformly exposed to the plasma whilesimultaneously allowing high-speed evacuation of process gas andsputtered contaminant species during a plasma processing operation.Vacuum distribution baffle 180 also prevents gas flow to vacuum pump 144from disturbing the position of workpiece 56 upon substrate support 64.

[0062] Preferably, vacuum distribution baffle 180 is formed of anelectrically-insulating material, such as a machinable ceramic, having aminimal out-gassing potential. Suitable machinable ceramics include analuminum oxide or a glass-bonded mica composite, such as Mykroy/Mycalex®or Macor®.

[0063] In one aspect of the present invention, chamber lid 14 integratesa gas distribution system that is configured to symmetrically and evenlydistribute the flowing stream of process gas over the surface ofworkpiece 56. Specifically, ceiling 28 of chamber lid 14 includes anembedded cavity 186, a process gas inlet port 190, and a plurality ofapertures 192. As best shown in FIG. 2C, gas inlet port 190 ispositioned in chamber lid 14 and is coupled via gas line 194 to a gasmanifold 308 (FIG. 4) for providing a process gas to processing space102. As best shown in FIG. 3, the vacuum side of ceiling 28 includesapertures 192 for injecting process gas from cavity 186 into processingspace 102. Preferably, apertures 192 are symmetrically distributed in atwo dimensional array about the longitudinal axis of processing chamber12 so that process gas will flow uniformly over the surface of workpiece56, and therefore, contribute to improving plasma uniformity.

[0064] In another aspect, chamber base 18 further includes a powerdistribution system that transfers electrical power from a plasmaexcitation source, such as radio-frequency (RF) generator 302 (FIG. 4),to ionize and dissociate the process gas confined within processingspace 102. The power distribution system includes a power distributionbar 198 operably connected to the RF generator 302, a pair of powerfeedthroughs 200 a,b, a bottom electrode 202, and substrate support 64.The RF generator 302 is operably connected by feedthroughs 200 a,b tothe substrate support 64, which serves as a powered electrode forcapacitively coupling excitation energy with the process gas inprocessing chamber 12 to initiate and sustain a plasma in processingspace 102. Chamber lid 14 and chamber base 18 collectively form anunpowered, ground electrode.

[0065] Floor wall 44 of chamber base 18 further includes two openings204 that receive power feedthroughs 200 a,b. A circular groove 208 isconcentrically disposed about the central, longitudinal axis of eachopening 204 for receiving an O-ring 210 therein. Each of the powerfeedthroughs 200 a,b includes an electrical tie rod 212 coaxiallysurrounded by a shield insulator washer 214, a chamber insulator washer216, and a bottom insulator washer 218. Preferably, washers 214, 216,218 are composed of a gas-impermeable ceramic dielectric, such as quartzor alumina, and each tie rod is formed of an electrical conductor, suchas copper, aluminum, or alloys thereof. Power feedthroughs 200 a,b areelectrically isolated from processing chamber 12.

[0066] Electrical tie rod 212 includes a flanged head 222 and an opposedthreaded end 226. Flanged head 222 is received within a complementaryrecess 228 disposed in the upper surface of bottom electrode 202 forelectrical continuity therewith and mechanical securement to inhibitdownward movement. Tie rod 212 extends downward through the centralbores in shield insulator washer 214, chamber insulator washer 216, andbottom insulator washer 218. Threaded end 226 protrudes beyond bottomwall 44 for connection with the excitation power supply.

[0067] Bottom insulator washer 218 includes an annular lower portion 232of a first outer diameter continuous with an annular upper portion 234of a lesser second outer diameter. Upper portion 234 is received withinopening 204 so that an upper surface of lower portion 232 abuts O-ring210 for a vacuum-tight seal with the non-vacuum surface of floor wall44. A frustoconical portion 236 of bore 230 is adapted to receive anO-ring 238. Frustoconical portion 236 is sized and configured so thatO-ring 238 can be compressed via fastener 239 to provide a vacuum sealbetween the circumference of tie rod 212 and bottom insulator washer218.

[0068] Shield insulator washer 214 is interposed between the lowersurface of bottom electrode 202 and the upper surface of vacuumdistribution baffle 180. Shield insulator washer 214 includes an annularlower portion 242 of a first diameter integral with an annular upperportion 244 of a greater second outer diameter. Upper portion 244 abutsvacuum distribution baffle 180 and lower portion 242 protrudes downwardinto an opening therein.

[0069] Chamber insulator washer 216 is interposed between the inner,bottom surface of the chamber base 18 and the lower surface of thevacuum distribution baffle 180. Chamber insulator washer 214 has opposedparallel surfaces 248, 250. Surface 248 includes a first recess that isadapted to fit over a length of upper portion 234 of bottom insulatorwasher 218. Opposed surface 250 includes a second recess of a diversediameter that receives a length of lower portion 242 of chamberinsulator washer 216.

[0070] Fastener 239 has a threaded bore adapted to mate with thethreaded end 226 of tie rod 212. When fastener 239 is tightened, anupper surface of bottom insulator washer 218 compressively engagesO-ring 210 and is urged upwardly thereagainst to create a vacuum-tightseal between the exterior of the chamber base 18 and bottom insulatorwasher 218. An upper surface of fastener 239 compressively engagesO-ring 238 disposed in frustoconical taper 234 to create a vacuum-tightseal between the circumference of tie rod 212 and the inner diameter ofbottom insulator washer 218.

[0071] Power distribution bar 198 is attached to threaded end 224 of tierod 212 by two fasteners 256, 258. The top surface of bottom electrode202 engages the lower surface of substrate support 64 in close contactso as to provide electrical continuity. Therefore, electrical powerapplied to the power distribution power 198 is transferred via tie rod212 to substrate support 64, which itself functions as a portion of thepowered electrode. Bottom electrode 202 and substrate support 64 arepreferably formed of an electrically-conductive material, such asaluminum. In an alternative embodiment, bottom electrode 202 may becomposed of a ceramic such that substrate support 64 alone constitutesthe powered electrode.

[0072] Vacuum distribution baffle 180, described in detail above, alsofunctions as a plasma shield that reduces the RF field strength betweenthe underside of bottom electrode 202 and chamber base 18. As a result,the plasma will be intensified near the surface of the workpiece 56 heldby substrate support 64 and the power and time to perform a plasmatreatment each workpiece 56 will be minimized. Further, theconfiguration of powered and ground electrodes produce an electric fieldsubstantially perpendicular to a workpiece 56 residing on substratesupport 64 such that ion trajectories are substantially perpendicular tothe surface normal of the workpiece 56.

[0073] Workpiece 56 is advantageously positioned in processing chamber12 having a vertical position substantially in a plane half-way betweenthe ceiling 28 of chamber lid 14 and the top surface of support platform68. Relative to known plasma treatment systems, minimization of thevolume of chamber 12 for a high pumping rate and precise positioning ofworkpiece 56 permit rapid plasma processing at a reduced power level.

[0074] Referring to FIG. 4, the plasma treatment system 10 includes agas flow control 300 and an RF generator 302 connected to the processingchamber 12. A treatment system control 304 receives input signals fromvarious devices within the plasma treatment system 10 and providesoutput signals to operate the gas flow control 300 and RF generator 302.The control 304 is also connected to a programmable graphics userinterface 306. The interface provides user input devices, for example,pushbuttons, switches, etc., and further, has output devices, forexample, lights and a display screen, thereby allowing the user tofollow the status of the operation of the plasma treatment system 10 andcontrol its operation. The control 304 may be any type of microprocessorbased control having both logic and arithmetic capabilities. Forexample, a programmable logic controller such as Model Direct Logic 205manufactured by Koyo and commercially available from Automation Directof Cummings, Ga. Further, the graphics user interface 306 is alsomanufactured by Koyo for the Direct Logic 205 and is also commerciallyavailable from Automation Direct.

[0075] Normally, during a plasma processing operation within theprocessing chamber 12, a plurality of process gases are mixed within amanifold 308. Exemplary process gases include Ar, He, CO₂, N₂, O₂, CF₄,SF₆, H₂, and mixtures thereof. Each process gas has an independent gassupply system 309 comprised of a gas source 310, a mass flow controller312, an isolation valve 314 and a solenoid valve 315. In the examplewhere two gases, for example, Ar and O₂, are used, there would be twoindependent gas supply systems 309 a, 309 b comprised of gas sources 310a, 310 b, mass flow controllers 312 a, 312 b, isolation valves 314 a,314 b and solenoid valves 315 a, 315 b. As will be appreciated, anynumber of additional gas supplies 309 n may be connected to the manifold308 and each additional gas will have its own gas source 310 n, massflow controller 312 n, isolation valve 314 n and solenoid valve 315 n.

[0076] In addition to independent gas supplies, the gas flow control 300includes vacuum pump 144, vacuum valve 140, solenoid valve 341 andpressure gauge 52. The plasma treatment system 10 is highly responsiveto changes in processing parameters. Therefore, pressure gauge 52 isplaced in close proximity to the chamber 12 and is fluidly connected tothe chamber 12 with tube 55 of an advantageously large diameter, forexample, a 0.500 inch diameter tube. The gas flow control 300 furtherincludes bleed valve 54 and its solenoid 357 for bringing the processingchamber 12 back to atmospheric pressure at the end of a plasmaprocessing cycle. Again, to minimize the depressurization process, bleedvalve 54 is normally in close proximity to the processing chamber 12 andhas a relatively large fluid communication opening therewith. Thus, thebleed valve 54 has the capability of returning the processing chamber 12to atmospheric pressure in approximately one second.

[0077] The RF generator 302 is comprised of an RF power supply 318providing RF power to an L-network tuner or impedance matching device320, for example, a pair of variable air capacitors. RF power supply 302operates at a frequency between about 40 kHz and about 13.56 MHz,preferably about 13.56 MHz, and a power between about 0 watts and about600 watts, preferably about 60 watts to about 400 watts. RF power fromthe variable air capacitors 320, 324 is applied over an output 328 tosubstrate support 64 (FIG. 3) within the processing chamber 12. A phasecapacitor 320 includes a movable plate connected to a motor 321 andfurther has a phase control 322 that provides an analog feedback signalon an input 323 of the control 304. A magnitude capacitor 324 has amovable plate connected to a motor 325 and further has a phase control326 that provides an analog feedback signal on an input 327 of thecontrol 304. The control 304 utilizes a known PID control loop toprovide analog command signals on outputs 328, 329 to the respectivemotors 321, 325 to move the plates of the variable air capacitors 320,324 in a known manner.

[0078] The PID control loop of the present invention utilizes a controlalgorithm that automatically provides a variable gain to improveperformance at the boundary conditions. The magnitude of the feedbacksignal on the input 323 has a range of from −5 volts to +5 volts; andwith a constant gain system, as the magnitude of the feedback signalmoves close to and through the zero crossing, accurate and stable systemcontrol is difficult. Traditionally, the gain is set to a fixed valuethat is a compromise between that needed to handle lower signal levelswhile not letting the control system saturate at higher signal levels.The result is a generally compromised or lower level of systemresponsiveness and performance, that is, the time required for thecontrol system to stabilize is longer. The present inventioncontinuously recalculates, and dynamically sets, a gain value as afunction of the signal strength of the feedback signal on the input 323.Thus, the PID loop is critically damped, that is, it reaches a stablestate quickly with a minimum of overshoot. In other respects, the tuningnetwork 320 functions in a known manner to match an impedance of an RFsystem comprised of an RF output of the RF power supply 318, the tuningnetwork 320 and the RF load presented by the RF circuit within theprocessing chamber 12 to a desired impedance value, for example, 50ohms.

[0079] As will be appreciated, various limit or proximity switches 330are utilized in association with the operation of the processing chamber12. For example, limit switches are utilized to detect the respectiveopened and closed positions of chamber lid 14 (FIG. 1) of the processingchamber 12 and provide a state feedback signal on a respective input 331of the control 304. Those limit switches may be connected to the lidactuator 122 (FIG. 2C) operating the lid 14, may be mounted on the lid14, or otherwise detect the position of the lid 14. A proximity switchis also used to detect the desired position of a workpiece 56 within theprocessing chamber 12. There are many different commercially availablelimit switch devices that utilize magnetism, mechanical contact, light,etc., to detect the proximity or position of an object. The choice of aparticular type of commercially available limit switch is dependent onthe application and preference of the designer.

[0080] An end point of a plasma processing cycle may be determined inseveral ways. The plasma treatment system of the present invention has avery high level of control; and therefore, the plasma processing cycleis highly repeatable. Hence, with the plasma treatment system of thepresent invention, the control 304 normally utilizes an internal timerto measure the duration of the plasma processing cycle. In someapplications, an end point detector 334 is operatively connected withthe processing chamber 12. The end point detector 334 is normally aphotoelectric switch that changes state in response to detecting adesired and particular wavelength of the light of the plasma generatedwithin the processing chamber 12. Visual communication between the endpoint detector 334 and the interior of the processing chamber 12 may beachieved by directing the end point detector 334 through the viewport 34(FIG. 1) or mounting the end point detector 334 within an opening orhole (not shown) in a wall of the processing chamber 12. Creation of thegas plasma within the processing chamber 12 produces light. Further, thewavelength of that light changes with the composition of the differentmaterials within the gas plasma in the chamber 12. For example, with anetching process, as the gas plasma etches different materials from thesurface of the workpiece, the wavelength of the light created by theplasma will be a function of a combination of the gas plasma and atomsof those materials. After any coatings and impurities have been etchedfrom the surface, continued etching will result in a combination ofatoms of the native material of the workpiece and the gas plasma. Thatcombination produces a unique wavelength of light which is detected bythe end point detector 334, and the detector 334 provides a binaryfeedback signal on an output 336 back to the control 304. Thus thecontrol 304 is able to detect when the plasma processing cycle iscompleted when that feedback signal changes state.

[0081]FIG. 5 is a flowchart illustrating the operation of the control304 in implementing a typical plasma processing cycle. At 602, a parttransfer cycle is initiated. During that process, the control 304provides command signals to a controller (not shown) that causes thepositioning lever 94 to move an unprocessed workpiece 56 into thechamber 12 between the side rails 78 a,b. As the part 56 is moved intoposition, one of the limit switches 330 detects the loaded position ofthe part and provides a state feedback on a respective output 331 to thecontrol 304. Upon the control, at 604, detecting a change in the switchstate indicating that the part is loaded, the control 304 provides acommand signal on an output 337 to open a solenoid valve 338. The opensolenoid 338 directs pressurized air from a pneumatic source, forexample, shop air, 340 to the lid actuator 122 in a direction causingthe lid actuator 122 to move the lid 14 to its closed position. One ofthe limit switches 330 detects the closed position, changes state andprovides a state feedback signal on a respective input 331 to thecontrol 304.

[0082] Upon detecting the lid closed position, at 608, the control 304then, at 610, provides a signal over an output 342 commanding thesolenoid 341 to open the vacuum valve 140. Simultaneously, at 612, thecontrol 304 establishes a pressure set point equal to PR_(PROCESS) andinitiates operation of a process pressure monitor. Normally, in a plasmatreatment system, the chamber 12 is evacuated to a desired and fixedpartial vacuum pressure prior to the start of a plasma processing cycle.However, the initial evacuation of the chamber 12 is a time consumingprocess. Applicants discovered that high quality plasma processing canbe undertaken within a range of pressures above and below a normallyused processing pressure within the chamber 12. The permissible pressurerange has been determined by processing many parts under differentconditions within the chamber 12. Thus, with the plasma treatment systemof the present invention an upper pressure boundary limit, for example,250 mTorr, is determined by adding an offset pressure, for example, 50mTorr, to the normally used processing pressure, for example, 200 mTorr.Further, a lower pressure boundary limit, for example, 150 mTorr, isdetermined by subtracting the offset pressure, for example, 50 mTorr,from the normally used processing pressure, for example, 200 mTorr. Inthis example, the pressure monitor system establishes the normally usedprocessing pressure of 200 mTorr as the pressure set point, but thepressure monitoring system will not set an alarm or otherwise impact theoperation of the plasma treatment process as long as the pressureremains between the upper and lower boundary limits of 250 mTorr and 150mTorr, respectively. Therefore, as long as the vacuum pump 144 isrunning, the control 304 is monitoring the input 348 which is providinga pressure feedback signal from the pressure gauge 52. When the control304 detects that the chamber 12 is evacuated to 250 mTorr, the gasplasma is started.

[0083] Simultaneously with starting the pressure monitor at 612, thecontrol 304, at 614, provides command signals over the outputs 344, 346to operate respective mass flow controllers 312 and isolation valves314. Process gas is introduced through process gas inlet port 190 at apredetermined flow rate, such as 5-100 standard cubic centimeters perminute (“sccm”) for Ar. The flow rate of gas provided by the mass flowcontrollers 312 and the pumping rate of the vacuum pump 144 are adjustedto provide a processing pressure suitable for plasma generation so thatsubsequent plasma processing may be sustained. Processing pressureswithin the chamber 12 are typically on the order of 50 to 1000 mTorr andpreferably in the range of 125 to 250 mTorr. In contrast to priorsystems, the processing chamber 12 is continuously evacuatedsimultaneously with the introduction of the process gases which areinitially used to purge ambient air from the chamber 12. In oneembodiment, the mass flow controllers 312 are operated to provide a flowrate of 30 sccm to the processing chamber which has a volume ofapproximately 0.50 liters. Thus, fresh gases are exchanged within theprocessing chamber 12 approximately four times per second. Moretraditional plasma treatment systems exchange the gas in the processingchamber approximately once every five seconds. The higher gas flow rateof the system of the present invention improves the removal of etchedmaterials and other contaminants from the processing chamber and alsominimizes the deposition of etched materials on the walls and toolingwithin the chamber 12.

[0084] The control 304 continuously monitors the feedback signal on theinput 348 from the pressure gauge 54 which is continuously measuring thepressure or partial vacuum within the processing chamber 12. At 616, thecontrol 304 detects when the pressure in the processing chamber 12 isequal to an initial pressure, that is, the normally used processingpressure plus the offset pressure value, which, in the example above is250 mTorr. The control then, at 618, provides a command signal on anoutput 350 to turn on the RF power supply 318. However, instead ofproviding full power from the RF power supply 318, the control 304commands the RF power supply to supply only a minimum power level, forexample, 30 watts. Traditional plasma treatment systems initially applyfull power to the processing chamber 12 via the tuning network 320.Creating the gas plasma at full power often results in plasma spikes,electric arcs, energy hot spots, other anomalies and a very unstable gasplasma. Further, since changes in the gas plasma result in a differentRF load in the processing chamber 12, the unstable gas plasma makes itvery difficult for the tuning network 320 to match the impedance of theRF system to a desired value. Consequently, by initially creating thegas plasma at full RF power, a substantial amount of time is consumedwaiting for the plasma to stabilize within the processing chamber 12 andthereafter, operating the tuning network 320 until the desired impedancematch is established. With the plasma treatment system of the presentinvention, initially applying a lower or minimum level of power, forexample, 30 watts, to the system permits the plasma in the chamber 12 tostabilize very quickly when compared to traditional systems.

[0085] After turning on the RF power supply 318 to the minimum powerlevel, the control 304, at 620, executes a 200 millisecond delay. Thisdelay period permits the plasma at the minimum power level to stabilize.Thereafter, at 622, the control 304 initiates the operation of anautomatic tuning cycle or autotune control by which the variable aircapacitors are used to match the RF impedance of the output of the powersupply 318 and the RF impedance of the input of the processing chamber12 to a desired impedance, for example, 50 ohms. During that process,analog feedback signals from the phase magnitude controls 322, 326 areprovided on respective inputs 323, 329 of the control 304. The controlexecutes a PID control loop and provides command signals on the outputs328, 329 to operate the respective motors 321, 325 such that thevariable air capacitors 320, 324 provide the desired impedance match.

[0086] The control then, at 624, determines whether the tuning network320 has achieved the desired impedance match. When that occurs, thecontrol 304, at 626, begins to ramp the power from its minimum level toa maximum level; and as the power is increased, the control, at 628,continues to operate the tuning network 320 with each successive powerlevel. Thus, as the control moves from its minimum power level to themaximum power level, the variable air capacitor 320 is continuouslyadjusted so that the impedance presented to the RF power supply 318remains matched to the desired 50 ohm load. Applicants have discoveredthat by maintaining the impedance match while ramping the RF power up tothe maximum level, a stabilized gas plasma is achieved at full power inless time than if the RF power supply 318 were initially turned on toits maximum power level and the impedance matching operation executed.

[0087] It should be noted that as the power is ramping up to its maximumlevel, the process gases are flowing through the processing chamber 12at their desired flow rates and the vacuum pump 144 is continuing todepressurize the processing chamber. As previously described, a range ofoperating pressure was determined by processing many workpieces usingdifferent process parameters. Using similar empirical methods, themaximum rate at which RF power can be increased while maintaining atuned RF system was also determined; and that maximum rate of RF powerincrease provides a reduced plasma treatment cycle.

[0088] If the control 304, at 630, determines the RF power is not at itsmaximum level, the control, at 628, again increments the power level andoperates the tuning network 320 to match the impedance to the desiredvalue. If, at 630, the control 304 determines that the power is now atits maximum value, the control then, at 632, begins monitoring for anendpoint of the plasma treatment cycle while the power remains at itsmaximum value and the plasma treatment process continues. During aplasma treatment operation, contaminant species sputtered from thesurface of workpiece 56 will be evacuated from processing space 102 viaexhaust port 136 along with the flowing stream of process gas. Plasmatreatment system 10 is optimized to enhance both the spatial uniformityof plasma treatment and system throughput.

[0089] The control 304, at 634, checks the state of the feedback signalon the input 352 from the end point detector 334 to determine whetherthe plasma processing cycle is complete. In the described embodiment,the endpoint of the processing cycle is determined by the endpointdetector 334 detecting a particular wavelength of light of the plasmaand providing a signal representing such to the control 304. As will beappreciated, by processing a large number of workpieces using differentprocessing parameters, the amount of time required to process aworkpiece can be determined. In an alternative embodiment, the control304 can start an internal timer at the same time that the autotunecontrol is started at 622. The timer is set to the amount of timerequired to process a workpiece as was empirically determined.Therefore, when the internal timer expires indicating an end of theplasma processing cycle, the control at 304 detects the expiration ofthe timer as the endpoint of the plasma treatment cycle.

[0090] Upon the control, at 634, detecting a state of the end pointfeedback signal on the input 352 representing an end of the plasmatreatment cycle, the control 304, at 636, provides a command signal onits output 350 to cause the RF power supply 318 to decrement or rampdown the RF power from its maximum level to its minimum level. Normally,the power is ramped down from its maximum level to its minimum level atthe same rate and thus, over an identical time period, as is required toramp the power up from its minimum level to its maximum level. Upon thecontrol 304 detecting, at 638, that the RF power supply 318 is providingpower at the minimum level, the control 304 then, at 640, the control304 checks that the RF system is tuned at the minimum power level.Thereafter, at 642, the control 304 turns off the autotune control andexecutes a 200 millisecond delay which permits the plasma at the minimumpower level to stabilize.

[0091] Traditional plasma processing cycles simply turn the RF generatoroff at the end of a processing cycle, and the tuning network is in astate corresponding to a processing power output from the RF powersupply. Hence, when the next cycle is started, which may be at adifferent power level, some time is required to for the tuning network320 to match the impedance. In contrast, with the present invention, atthe end of a cycle, the tuning network is tuned to minimum power. Thus,at the start of the next processing cycle, when the RF power supply 318is turned on to minimum power, the tuning network 320 is in a state suchthat, either, the desired impedance match already exists, or it can bequickly tuned to a match. Minimizing tuning of the RF system can resultin cycle time savings of up to 15 seconds.

[0092] Next, the control 304, at 644, stops the operation of thepressure monitor and provides command signals on the outputs 342 and 346to cause respective solenoid valves 341 and 315 to close the respectivevacuum valve 140 and isolation valves 314. Further, the control 304provides a command signal on output 344 to terminate the flowrate ofgases through the appropriate mass flow controllers 312. In addition,the control 304 provides a command signal over an output 356 to causesolenoid valve 357 to open the bleed valve 54, thereby depressurizingthe processing chamber 12. At 646, the control 304 determines that thepressure within the processing chamber 12 is substantially equal toatmospheric pressure. This determination is normally made by the controlusing an internal timer to measure a period of time required todepressurize the processing chamber 12 with the bleed valve 54.Thereafter, at 648, the control 304 provides a command signal on theoutput 337 causing the solenoid valve 338 to change state and reversethe operation of the lid actuator 122. Thereafter, at 650, the control304 detects that the lid 14 is raised to its opened position andinitiates a successive part transfer cycle 602. The above process isthen repeated for successive workpieces.

[0093]FIGS. 6 and 7 depict an alternative embodiment of the processingchamber 12 according to the principles of the present invention whichincludes a variable-width substrate support 260. Support 260advantageously permits workpieces of variable dimension to be receivedthereon. Referring to FIG. 6, substrate support 260 includes an elevatedplatform 262 that slideably carries two moveable opposed side rails 264,266 and a flat plate 267 that is attached to bottom electrode 202 by thedownward force applied by each tie rod 212. Elevated platform 262 ismechanically and electrically attached by a plurality of fasteners 269to flat plate 267. As shown by arrows 268, 270, side rails 264, 266 aremoveable between an extreme position near the perimeter of supportplatform 262 to a central position along the longitudinal axis ofelevated platform 262. As a result, the separation distance betweensides rails 264, 266 may be varied to accommodate a workpiece 272 of apredetermined transverse width.

[0094] Side rail 264 and side rail 266 are identical structures thatwill be described with reference to side rail 266. Referring to FIG. 7,side rail 266 comprises a horizontal member 274 flanked at each opposedend by an integral vertical post 276. A channel 278 extendslongitudinally along the entire length of horizontal member 274 and hasa U-shaped cross-section with a predetermined width that accepts aperipheral edge of workpiece 272. Each opposed end of channel 278includes a flared lip 280 that facilitates slideable capture of sideedges of the workpiece 272.

[0095] Each vertical post 276 includes an upper prong 282 with athreaded bore 284 for receiving a set screw 286 and a beveled lowerprong 288. The lower surface of upper 282 prong is displaced verticallyfrom the upper surface of lower prong 288 to create an indentation 290of a width that is slightly less than the thickness of elevated platform262. The indentation 290 slideably receives a peripheral edge ofelevated platform 262. Accordingly, each side rail 264, 266 may beindependently moved to a predetermined transverse position and affixedwith set screw 286.

[0096] With reference to FIGS. 8-12 in which like reference numeralsrefer to like features in FIGS. 1-7 and according to an alternativeembodiment of the invention, the plasma treatment system 10 may beprovided with a processing chamber 400 including the chamber base 18 anda chamber lid 402 hingeably coupled with the chamber base 18.Specifically, one side of chamber lid 402 is mounted to hinge assembly16 so that chamber lid 402 may be selectively pivoted or cantileveredrelative to chamber base 18 between an open positioned for transferringworkpiece 56 into or out of the processing space 102 and a closedposition in which the chamber lid 402 makes a sealing contact withchamber base 18. Loading station 20 (FIG. 1) and exit station 22(FIG. 1) may be used for shuttling workpieces 56 into and out ofprocessing chamber 400 as described herein with regard to processingchamber 12. Chamber lid 402 may be interchanged with chamber lid 14(FIG. 1) for expanding the capabilities of the plasma treatment system10. It follows that an existing plasma treatment system having anoriginal chamber lid may be retrofitted with a substitute chamber lidincorporating the inventive aspects of chamber lid 402.

[0097] The chamber lid 402 is an assembly that includes a lower sidewallsection 404, a domed ceiling section 406, and a medial sidewall section408 separating the lower sidewall section 404 from the domed ceilingsection 406. The sidewall sections 404 and 408 and the domed ceilingsection 406 are formed of a material that has a relatively highelectrical conductivity, such as an aluminum or aluminum alloy. Acompressible elastomeric O-ring seal 401 is provided between acircumferential upper rim of the medial sidewall section 408 and acircumferential lower rim of the upper domed section 406. Anothercompressible elastomeric O-ring seal 403 is provided between acircumferential lower rim of the medial sidewall section 408 and acircumferential upper rim of lower sidewall section 404. O-ring 51 iscompressively captured between a circumferential lower rim of the lowersidewall section 404 and an apron of chamber base 18. The lower sidewallsection 404 includes two view port assemblies, of which view portassembly 410 is visible in FIG. 12, for viewing the plasma processestranspiring in the processing space 102 of processing chamber 400.

[0098] Provided in a dividing wall 406 a of the domed ceiling section406 separating plasma cavity 442 from a radio-frequency (RF) cavity 472is a gas port 409. The gas port 409 is configured with a gas fitting 411that couples a plasma cavity 442 in fluid communication with a gas line405 extending to a source 407 of a process gas. The gas fitting 411 iscoupled with plasma cavity 442 by a gas distribution path including aprocess gas passageway 413, a pair of process gas passageways 415a,bcoupled with process gas passageway 413, and multiple gas passageways417 extending from gas passageways 415 a,b so as to terminate proximatethe upper planar surface of a ceramic insulator plate 416. Any suitableprocess gas or process gas mixture may be provided that is capable ofproviding free radicals and other reactive species, when excited by RFenergy to generate a plasma, appropriate to perform a downstream-typeplasma treatment of workpieces 56, as described herein. Typical processgases include O₂, CF₄, N₂ and H₂ and may be mixed with an inert gas,such as Ar, to provide a process gas mixture. A gas flow rate suitablefor downstream-type plasma treatment in processing chamber 400 generallyranges from about 1 sccm to about 300 sccm and an appropriate pressurein plasma cavity 442 ranges from about 50 mTorr to about 1000 mTorr.

[0099] A mass-flow-controlled flow of ambient air from the surroundingenvironment of processing chamber 400 may be used as a process gas andhas been found to be particularly effective in certain applications forremoval of surface contamination. Such a downstream-type plasma isexpected to contain free radicals, including oxygen-based andnitrogen-based free radicals, derived from hydrogen, oxygen, nitrogenand other primary constituents of air.

[0100] With continued reference to FIGS. 8-12, the domed ceiling section406 of chamber lid 402 is provided with a grounded plate 412 and apowered electrode 414 that defines a powered plane oppositeand-generally parallel to grounded plate 412. The grounded plate 412 andthe portions of the domed ceiling section 406 surrounding plasma cavity442 collectively define a ground plane. A rectangular, planar ceramicelectrode insulator 416 electrically isolates the powered electrode 414from the domed ceiling section 406, including grounded plate 412. Plasmacavity 442 is defined in the domed ceiling section 406 as a volumeenclosed between the grounded plate 412 and the powered electrode 414.The grounded plate 412 and the powered electrode 414 are each formed ofa material having a high electrical conductivity, such as aluminum or analuminum alloy.

[0101] Grounded plate 412 includes a plurality of openings orthroughholes 421 (FIG. 13) having a configuration, dimension, and/orarrangement dependent upon the geometrical shape of the workpiece 56.The throughholes 421 allow the preferential transmission of freeradicals, and other process gas species lacking a net charge, from adirect plasma created in plasma cavity 442 to the processing space 102and prohibit or prevent the transfer of charged species, such as ionsand electrons, from the direct plasma residing in plasma cavity 442 toprocessing space 102. Typically, the grounded plate 412 is effective forremoving a significant percentage of the charged species from the plasmaadmitted from plasma cavity 442 into the processing space 102. Thethroughholes 421 may present tortuous paths having no line-of-sightpaths from the plasma cavity 442 to the processing space 102. The plasmain processing space 102 is a downstream-type plasma that is free, orsubstantially free, of charged particles for performing plasmatreatments of the workpiece 56 by the chemical action of the radicalswithout the physical action otherwise provided by the charged particles.

[0102] The throughholes 421 may be arranged in an array or matrix or maybe arranged with non-periodic center-to-center hole spacings. The arealdensity of throughholes 421 in the grounded plate 412 may range fromabout ten (10) holes per square inch to about two hundred (200) holesper square inch. The diameter of individual throughholes 421 may rangefrom about 0.001 inches to about 0.125 inches.

[0103] With reference to FIGS. 13 and 14, the chamber lid 402 may bereconfigured using other grounded plates, such as grounded plate 418(FIG. 13) and grounded plate 420 (FIG. 14). Grounded plates 418, 420 areinterchangeable with grounded plate 412 for varying the distribution orpattern of free radicals delivered from the direct plasma in plasmacavity 442 to processing space 102 and, ultimately, delivered to anexposed surface 56 a of workpiece 56 supported on substrate support 64.The throughholes 419 in grounded plates 418 and 420 differ inconfiguration, dimension and/or arrangement from grounded plate 412 forvarying the spatial distribution of free radicals admitted from plasmacavity 442 into processing space 102.

[0104] Grounded plate 418 includes a plurality of throughholes 419arranged inside the circular outer periphery of a disk-shaped holepattern. Grounded plate 418 may be used, for example, to treatsemiconductor wafers, such as 300 mm silicon wafers, with adownstream-type plasma. Grounded plate 420 includes two frame plates422, 424 having a rectangular central opening and a screen or grid 426captured between frame plates 422, 424 so as to partially occlude thecentral opening. The screen 426 is a fine wire mesh made from a materialwith relatively high electrical conductivity, such as aluminum or analuminum alloy.

[0105] The ability to select from among various grounded plates 412, 418and 420 permits tailoring of the geometrical pattern of radicalsdelivered from the plasma to the workpiece 56. To that end, the holepattern of throughholes, such as throughholes 421 of grounded plate 412,can be adjusted to correspond to the geometry of the workpiece 56 beingplasma treated with the downstream-type plasma. For example, thethroughholes 421 in the grounded plate 412 can be arranged in adisk-shaped hole pattern for processing round workpieces, asquare-shaped hole pattern for square workpieces, a rectangular holepattern for rectangular workpieces, and other geometrical arrangementsapparent to persons of ordinary skill in the art as necessary tocorrespond with the geometrical shape of the workpiece 56. Typically,the throughholes 421 are positioned in the grounded plate 412 so thatthe peripheral extent of the hole pattern corresponds substantially tothe outer peripheral rim or circumference of the workpiece 56.

[0106] With reference to FIGS. 8-12, the chamber lid 402 furtherincludes a radio-frequency (RF) bulkhead fitting 428, a pair of ceramiccaps 430 a,b, a pair of annular ceramic spools 432 a,b, a pair of powerfeedthroughs 434 a,b, a power distribution bar 436, and aradio-frequency (RF) lid closure element 438. A radio-frequency (RF)power supply 439 is electrically coupled by a transmission line 440 withthe RF bulkhead fitting 428. The RF power supply 439 and the componentsof the chamber lid 402 collectively provide a plasma excitation sourcecapable of exciting process gas in the plasma cavity 442 to generate aplasma. Power feedthroughs 434 a,b transfer RF power from the RFbulkhead fitting 428 and power distribution bar 436 to the poweredelectrode 414. The RF power supply 439 typically operates at a frequencybetween about 40 kHz and about 13.56 MHz, preferably about 13.56 MHz,and a power between about 0 watts and about 600 watts, typically about50 watts to about 600 watts.

[0107] Ceramic cap 430 a is fastened to the top of power feedthrough 434a and is positioned between power distribution bar 436 and closureelement 438. Ceramic spool 432 a is captured between the dividing wall406 a and the power distribution bar 436, and power feedthrough 434 aextends through the bore of ceramic spool 432 a to establish electricalcontact between the power distribution bar 436 and the powered electrode414. Ceramic cap 430 b is fastened to the top of power feedthrough 434 band is positioned between power distribution bar 436 and closure element438. Ceramic spool 432 b is captured between the dividing wall 406 a,and the power distribution bar 436 and power feedthrough 434 b extendsthrough the bore of ceramic spool 432 b to establish electrical contactbetween the power distribution bar 436 and the powered electrode 414.The ceramic caps 430 a,b cooperate to electrically isolate the power bar436 and upper ends of the power feedthroughs 434 a,b from the closureelement 438. The ceramic spools 432 a,b cooperate to electricallyisolate the power feedthroughs 434 a,b from the dividing wall 406 a ofdomed ceiling section 406. Ceramic spools 432 a,b also maintain a smallgap in the vertical dimension between the ceramic insulator plate 416and the dividing wall 406 a so that gas flow can occur therebetween.

[0108] In use and with continued reference to FIGS. 8-12, process gasenters the chamber lid 402 through the gas fitting 411 and is directedthrough gas passageways 413, 415 a,b to the multiple gas passageways 417terminating on the upper side of the ceramic insulator plate 416. Theprocess gas flows or seeps around the periphery or perimeter of thepowered electrode 414 and the ceramic insulator plate 416 so the flow ofprocess gas is directed toward the outer edges of the domed ceilingsection 406. The process gas is attracted laterally by vacuum forces inthe processing space 102 about the edges of the ceramic insulator plate416 and toward the throughholes 421, which promotes uniform process gasdistribution in the plasma cavity 442.

[0109] The RF energy applied between the grounded plate 412 and thepowered electrode 414 ignites and sustains a plasma from the process gasresiding in plasma cavity 442. The plasma in plasma cavity 442 is a fulldirect plasma containing ions, electrons, free radicals and molecularspecies. Because the flow of process gas in the plasma treatment system10 is generally conducted toward exhaust port 136 in bottom wall 44, thevarious components of the direct plasma in plasma cavity 442 will beattracted by a suction or vacuum force toward the throughholes 421 ofgrounded plate 412. The electrons and ions have a tendency to recombineinside throughholes 421 because grounded plate 412 is grounded relativeto earth ground. As a result, the ions and electrons are significantlyless likely to enter processing space 102. The grounded plate 412permits plasma species lacking a net charge, such as free radicals andneutral molecules, to be transported through throughholes 421 into theprocessing space 102. Typically, the grounded plate 412 is effective forremoving substantially all of the charged species from the plasmatransferred or admitted from plasma cavity 442 into the processing space102

[0110] The vacuum or the pumping action of vacuum pump 144 (FIG. 3)urges the free radicals and neutral molecules toward the workpiece 56 toperform the downstream-type plasma treatment. The workpiece 56 to betreated with the downstream-type plasma is supported by the side rails66 a, 66 b of substrate support 64. Free radicals admitted intoprocessing space 102 contact with the exposed surface 56 a of workpiece56 and react chemically with the material forming the workpiece 56 toperform the surface treatment. Excess free radicals, unreactive processgas molecules, and contaminants removed from the workpiece 56 areexhausted from the processing space 102 by the pumping action of vacuumpump 144.

[0111] Chamber lid 402 provides the plasma processing system 10 withvarious different capabilities in addition to the ability to generate adownstream-type plasma for surface treatments. Because the groundedplate 412 provides a ground plane, substrate support 64 may be energizedby RF generator 302 (FIG. 4) to generate a direct plasma in processingspace 102. It follows that a plasma treatment system, such as plasmatreatment system 10, which is equipped with chamber lid 402, may be usedto selectively plasma treat workpieces 56 with either a direct plasma ora downstream-type plasma, as required by the process, so that bothcapabilities are available in a single system 10.

[0112] In an alternative mode of operation, the plasma treatment system10 can be configured to provide an inverted direct plasma by removingthe grounded plate 412, grounding the substrate support 64 to earthground, and energizing the powered electrode 414 to generate a directplasma in processing space 102 and plasma cavity 442. With the groundedplate 412 removed, the chamber configuration changes so that the poweredplane is provided by powered electrode 414 and the ground plane isprovided by the substrate support 64. The inverted direct plasmaconfiguration reduces the process time, under certain circumstances, forimproving the plasma treatment of the upper exposed surface 56 a of theworkpiece 56.

[0113] In another mode of operation, the plasma treatment system 10 canbe configured to power the powered electrode 414 with the grounded plate412 removed and, in addition, to energize the substrate support 64, asdescribed herein. In this mode of operation, the RF power provided by RFpower supply 439 to electrode 414 is driven 180° degrees out of phaserelative to the RF power provided by generator 302 (FIG. 4) to thesubstrate support 64. As a result, the voltage potential providing thedriving force for ionizing the process gas in processing space 102 (FIG.3) is effectively doubled for an equivalent overall amount of RF power.One potential benefit of this mode of operation is that the RF powerapplied to substrate support 64 is reduced due to the direct plasmaelectrons and ions supplied when the powered electrode 414 is energized.

[0114] In yet another mode of operation, the plasma treatment system 10can be configured to power the powered electrode 414 with the groundedplate 412 installed and, in addition, to energize the substrate support64, as described herein. In this operational mode, the workpiece 56 willbe exposed to direct plasma generated in the processing space 102infused with free radicals from the direct plasma in plasma cavity 442admitted after filtering of charged particles by grounded plate 412 intoprocessing space 102. According to the principles of the invention, theprocess gas flowing from process gas source 407 into the plasma cavity442 may differ from the process gas flowing directly into processingspace 102 from an independent process gas source (not shown) so that thefree radicals transferred to the processing space 102 through thegrounded plate 412 from plasma cavity 442 differ from the species in thedirect plasma generated in processing space 102.

[0115] According to the principles of the invention and with continuedreference to FIGS. 8-12, medial sidewall section 408 is operative forincreasing the chamber dimension of the chamber lid 402 in the verticaldirection. The chamber dimension in the vertical direction may bereduced by removing the medial sidewall section 408 from the chamber lid402. Additional medial sidewall sections 408 may be added or stackedbetween the original medial sidewall section 408 to further increase theheight of the chamber lid 402 and to further expand the chamberdimension in the vertical direction. It is further contemplated by theinvention that the vertical dimension of the chamber lid 402 may bevaried in any of multiple different manners, such as by constructing themedial sidewall section 408 as an expandable vacuum bellows. The lowersidewall section 404 and a domed ceiling section 406 are always presentin the assembly forming chamber lid 402 and, when assembled in theabsence of the medial sidewall section 408, the dimensions of sections404 and 406 define a minimum separation between the powered electrode414 and the exposed surface 56 a of workpiece 56 confronting the poweredelectrode 414.

[0116] The medial sidewall section 408 is removably mounted to the lowersidewall section 404. Guides 444 are provided to aid in positioning themedial sidewall section 408 relative to the lower sidewall section 404during installation. Similarly, guides 444 aid the positioning of domedceiling section 406 relative to the medial sidewall section 408 duringinstallation. Guides 444 may also be used for positioning the domedceiling section 406 relative to the lower sidewall section 404 if themedial sidewall section 408 is removed from the assembly. Fasteners 448are utilized for securing the medial sidewall section 408 with the lowersidewall section 404 and for applying a compression force to O-ring 403to create a vacuum-tight seal. Similarly, fasteners 450 are utilized forsecuring the domed ceiling section 406 with the medial sidewall section408 and for applying a compression force to O-ring 401 to create avacuum-tight seal.

[0117] The ability to vary the chamber dimension of processing chamber400 in the vertical direction by inserting and removing one or more ofthe medial sidewall sections 408 permits the plasma treatment system 10to accommodate workpieces 56 of differing thickness. Specifically, areproducible or predictable distance or separation can be maintainedbetween the powered electrode 414 and the exposed surface 56 a of theworkpiece 56 held by the substrate support 64. To that end, the verticaldimension of each medial sidewall section 408 may be selected to providea desired separation between powered electrode 414 and exposed surface56 a. For example, configuring the chamber lid 402 with two one-inchthick medial sidewall sections 408 will separate the exposed surface 56a of a two-inch thick workpiece 56 from powered electrode 414 by thesame distance as a one-inch thick workpiece 56 in a process chamberconfiguration in which the chamber lid 402 has a single one-inch medialsidewall section 408.

[0118] The separation between the treated surface of the workpiece 56and the powered electrode 414 is a fundamental variable that must becontrolled for effective plasma treatment with either a direct plasma ora downstream-type plasma in which the treatment uniformity is adequate.It is appreciated that the capability of changing the enclosed volume ofthe chamber lid 402 and the processing space 102 using one or more ofthe removable medial sidewall sections 408 is applicable withoutlimitation for both direct plasma and downstream-type plasma treatmentsystems.

[0119] With reference to FIGS. 15-18 in which like reference numeralsrefer to like features in FIGS. 1-14 and according to an alternativeembodiment of the invention, the plasma treatment system 10 may beprovided with a processing chamber 500 including the chamber base 18 anda chamber lid 502, similar to chamber lid 402, that is hingeably coupledwith the chamber base 18. Chamber lid 502 is mounted to hinge assembly16 for selectively pivoting or cantilevering relative to chamber base 18between an open positioned for transferring workpiece 56 into or out ofthe processing space 102 and a closed position in which the chamber lid502 sealingly contacts chamber base 18. Chamber lid 502 may beinterchanged with chamber lid 14 (FIG. 1) or with chamber lid 402 (FIGS.8-14) for expanding the capabilities of the plasma treatment system 10in a manner similar to chamber lid 502 and may be retrofitted to anexisting plasma treatment system, such as plasma treatment system 10.

[0120] Chamber lid 502 is an assembly including a domed ceiling section504 having a plasma cavity 542 and a lower sidewall section 506 fastenedwith the domed ceiling section 504. The domed ceiling section 504includes a sidewall 501 extending about the periphery of the plasmacavity 542 and a dividing wall 508 separating a radio-frequency (RF)chamber 543 from the plasma cavity 542. Guides 544 (FIG. 16) are usedfor positioning the domed ceiling section 504 relative to the lowersidewall section 506. A compressible elastomeric O-ring seal 503 isprovided between a circumferential lower rim of the domed ceilingsection 504 and a circumferential upper rim of lower sidewall section506. Fasteners 448 are utilized for securing the domed ceiling section504 with the lower sidewall section 506 and for applying a compressionforce to O-ring 503 to create a vacuum-tight seal. O-ring 51 iscompressively captured between a circumferential lower rim of the lowersidewall section 506 and an apron of chamber base 18 to provide avacuum-tight seal thereat. The lower sidewall section 506 includes aview port assembly 510 incorporating a site glass that allows anobserver to view the plasma processes transpiring in the processingspace 102 of processing chamber 500. It is contemplated by the inventionthat one or more medial sidewall sections (not shown), similar to medialsidewall sections 408 (FIGS. 8-12) described herein, may be introducedbetween the domed ceiling section 504 and the lower sidewall section506.

[0121] With continued reference to FIGS. 15-18, a gas line 505 couples aprocess gas source 507 (FIG. 16) via a gas fitting 511 with a gas port509 provided in the domed ceiling section 504. The gas port 509 iscoupled in fluid communication with plasma cavity 542 defined in chamberlid 502 by a gas distribution path that includes a process gaspassageway 513 and a gas distribution baffle 546 defining a gasdistribution chamber 515 coupled in fluid communication with process gaspassageway 513. The gas distribution chamber 515 is coupled in fluidcommunication with the plasma cavity 542 by a distributed arrangement ofmultiple gas outlets 517 in the gas distribution baffle 546. The gasoutlets 517 may assume any dimensions or arrangement to provide a gasload suitable for tailoring the plasma admitted into processing space102 for plasma treating different types and configurations of workpieces56. Any suitable process gas or process gas mixture may be provided toplasma cavity 542 that is capable of providing free radicals and otherreactive species, when excited by RF energy to generate a direct plasmain plasma cavity 542, appropriate to perform a downstream-type plasmatreatment of workpieces 56, as described herein. The inventioncontemplates that the gas distribution baffle 546 may be omitted andthat the flow of process gas may enter the plasma cavity 542 through theoutlet of process gas passageway 513. To that end, the outlet of processgas passageway 513 may be positioned to approximately coincide with thegeometrical center of the domed ceiling section 504.

[0122] The domed ceiling section 504 is provided with a grounded plate512 and a powered electrode 514 spaced vertically from the groundedplate 512. The powered electrode 514 defines a powered plane in theplasma cavity 542 that is opposite and generally parallel to thegrounded plate 512. The grounded plate 512 has a good electrical contactwith sidewall 501 that electrically grounds grounded plate 512 as thechamber lid 502 is grounded. The grounded plate 512 and the portions ofthe domed ceiling section 504 surrounding plasma cavity 542 collectivelydefine a ground plane. The grounded plate 512 and the powered electrode514 are each formed of a material having a high electrical conductivity,such as aluminum or an aluminum alloy.

[0123] With continued reference to FIGS. 15-18, grounded plate 512 is anassembly that includes an upper slotted plate 516, a center slottedplate 518, and a lower slotted plate 520. The plates 516, 518, and 520are of substantially equal thickness, although the invention is not solimited. The upper slotted plate 516 is perforated with multipleopenings or slots 522 having a major axis extending transversely to amachine direction, into and out of the plane of the page of FIG. 16, inwhich workpieces 56 are transported from loading station 20 to substratesupport 64 and from substrate support 64 to exit station 22. Similarly,the center and lower slotted plates 518, 520 are each perforated withmultiple openings or slots 524, 526, respectively, each having a majoraxis extending transversely to the machine direction for workpiecetransport. The cross-sectional profile of each of the slots 522, 524,526, when viewed vertically, may be any shape having a major axisaligned transverse to the machine direction and, in particular, may beeither rectangular or oval.

[0124] With reference to FIGS. 15 and 15A, slots 522 and 526 of theupper and lower slotted plates 516 and 520, respectively, are alignedvertically. The slots 524 of the center slotted plate 518 are offsetfrom slots 522 and 526 in the machine direction. The slots 522, 524, and526 permit a fluid flow of process gas and radicals from the plasmacavity 542 to the processing space 102, but present a tortuous orlabyrinthine path that substantially eliminates all line-of-sight pathsfrom the processing space 102 to the plasma cavity 542 in cooperationwith the relative inter-plate spacings between slotted plates 516 and518 and between slotted plates 518 and 520. The elimination ofline-of-sight paths prevents light, typically in the visible region ofthe electromagnetic spectrum, generated by the direct plasma in plasmacavity 542, from entering the processing space 102, other than lightredirected by reflection.

[0125] With reference to FIGS. 15, 16 and 18, upper slotted plate 516 isspaced from the center slotted plate 518 by a plurality of, for example,four peripherally-arranged spacers 550 that supply a good electricalcontact between plates 516 and 518. Similarly, lower slotted plate 520is spaced from the center slotted plate 518 by a plurality of, forexample, four peripherally-arranged spacers 551 that provide a goodelectrical contact between plates 518 and 520. Spacers 550 aredimensioned for separating plates 516 and 518 by a uniform gap and,similarly, spacers 551 are dimensioned for separating plates 518 and 520by a uniform gap that may differ from the gap between plates 516 and518.

[0126] It is contemplated by the invention that the slots 522, 524 and526 may have any relative spatial arrangement that, in cooperation withthe inter-plate spacings, eliminates, prohibits, or at leastsubstantially reduces, line-of-sight paths between the plasma cavity 542and the processing space 102. The invention also contemplates that theslots 522, 524, 526 may have a configuration, dimension, and/orarrangement compliant with the geometrical shape of the workpiece 56. Inone embodiment, the slots 522, 524 and 526 are rectangular incross-sectional profile viewed in a direction extending betweenprocessing space 102 and plasma cavity 542 and have a dimension alongtheir major axis of approximately two (2) inches, a dimension alongtheir minor axis of approximately {fraction (3/16)} inches, a spacingbetween adjacent slots of about {fraction (3/32)} inches, and the slots524 are offset from slots 522 and slots 526 by {fraction (3/16)} inches.The upper and center plates 516 and 518 are separated by a distanceapproximately equal to the plate thickness and the center and lowerplates 518 and 520 are separated by a distance approximately equal to1.5 times the plate thickness.

[0127] The grounded plate 512 prohibits the transfer of charged species,including ions and electrons, from the direct plasma in the plasmacavity 542 to the processing space 102 and allows the transfer of freeradicals, and other process gas species lacking a net charge, from theplasma cavity 542 to the processing space 102. Specifically, the chargedspecies are captured by the material of the slotted plates 516, 518, 520surrounding the slots 522, 524, 526, respectively, which are grounded.The pumping action of vacuum pump 144 (FIG. 3) attracts the freeradicals and neutral molecules through the slots 522, 524, 526 fromplasma cavity 542 into the processing space 102 and toward the workpiece56 to perform the downstream-type plasma treatment. The plasma inprocessing space 102 is a downstream-type plasma that is free, orsubstantially free, of charged particles and light for performing plasmatreatments of the workpiece 56 by the chemical action of the radicalswithout the physical action otherwise provided by the charged particles.Typically, the grounded plate 512 is effective for removingsubstantially all of the charged species from the portion of the directplasma transferred or admitted from plasma cavity 542 into theprocessing space 102. Typically, the grounded plate 512 is effective forremoving at least about 90% of the charged particles and may beeffective for removing 99% or more of the charged particles.

[0128] Grounded plate 512 is configured to be removable from the chamberlid 502 for changing the configuration, dimension, and/or arrangement ofslots 522, 524, 526 to accommodate, for example, a change in the type ofworkpiece 56 being plasma treated, as described herein with regard togrounded plates 412, 418 and 420 (FIGS. 12-14). For example, the slots522, 524, 526 may be dimensioned and arranged in a disk-shaped patternfor processing round workpieces, a square-shaped pattern for squareworkpieces, a rectangular pattern for rectangular workpieces, and othergeometrical arrangements apparent to persons of ordinary skill in theart as necessary to correlate with the geometrical shape of theworkpiece 56.

[0129] With reference to FIGS. 15-18, the chamber lid 502 furtherincludes a radio-frequency (RF) bulkhead fitting 528, a pair ofelectrically-insulating caps 530 a,b, a pair of dielectric spools 532a,b, a pair of power feedthroughs 534 a,b, a power distribution bar 536,a removable radio-frequency (RF) lid closure element 538 that affordsaccess to RF chamber 543, and a pair of annular ceramic spacers 540 a,b.A radio-frequency (RF) power supply 539 is electrically coupled by atransmission line 540 with the RF bulkhead fitting 528. The RF powersupply 539 and the components of the chamber lid 502 collectivelyprovide a plasma excitation source capable of exciting process gas inthe plasma cavity 542 to generate a plasma. Power feedthroughs 534 a,btransfer RF power from the RF bulkhead fitting 528 and powerdistribution bar 536 to the powered electrode 514. The RF power supply539 typically operates at a frequency between about 40 kHz and about13.56 MHz, preferably about 13.56 MHz, and a power between about 0 wattsand about 600 watts, typically about 50 watts to about 600 watts.

[0130] The power feedthroughs 534 a,b and ceramic spools 532 a,b arepositioned in respective openings 541 a,b extending through dividingwall 508. Cap 530 a is fastened to the top of power feedthrough 534 aand is positioned between power distribution bar 536 and closure element538. Ceramic spool 532 a has a flange that is captured between thedividing wall 508 and the power distribution bar 536, and powerfeedthrough 534 a extends through the bore of ceramic spool 532 a toestablish electrical contact between the power distribution bar 536 andthe powered electrode 514. Cap 530 b is fastened to the top of powerfeedthrough 534 b and is positioned between power distribution bar 536and closure element 538. Ceramic spool 532 b has a flange capturedbetween the dividing wall 508 and the power distribution bar 536, andpower feedthrough 534 b extends through the bore of ceramic spool 532 bto establish electrical contact between the power distribution bar 536and the powered electrode 514. The ceramic spacer 540 a is capturedbetween the dividing wall 508 and the powered electrode 514 and isconcentric with ceramic spool 532 a. Similarly, the ceramic spacer 540 bis captured between the dividing wall 508 and the powered electrode 514and is concentric with ceramic spool 532 b. The caps 530 a,b cooperateto electrically isolate the power bar 536 and upper ends of the powerfeedthroughs 534 a,b from the closure element 538. The ceramic spools532 a,b and the ceramic spacers 540 a,b cooperate to electricallyisolate the power feedthroughs 534 a,b from the dividing wall 508 ofdomed ceiling section 504.

[0131] With continued reference to FIGS. 15-18, the powered electrode514 is positioned within the plasma cavity 542 such that its planarupper surface 514 a, planar lower surface 514 b and side edge 514 c arepositioned substantially equidistantly from adjacent surroundingsurfaces of the domed ceiling section 504 and the grounded plate 512that are electrically grounded. Specifically, upper surface 514 a isseparated vertically from, and in a generally parallel relationshipwith, a downwardly-facing planar surface 546 a of gas distributionbaffle 546 by approximately the same distance that lower surface 514 bis separated from an upwardly-facing planar surface 516 a of the upperslotted plate 516. The surfaces 514 b and 516 a have a generallyparallel relationship. In addition, the transverse distance between theside surface 514 c and adjacent portions of an inwardly-facing surface501 a of side wall 501 is approximately equal to the separations betweensurfaces 514 a and 546 a and surfaces 514 b and 516 a. It follows thatthe powered electrode 514 is symmetrically positioned relative to andequidistant from surfaces 501 a, 546 a and 516 a. In one specificembodiment that provides a particularly uniform plasma in plasma cavity542 and, consequently, a particularly uniform downstream-type plasma inprocessing space 102, the separations between the powered electrode 514and surfaces 501 a, 546 a and 516 a are each approximately one (1) inch.The equidistant spacing and the magnitude of the spacing cooperate topermit application of full power, without ramping, from RF power supply539 to the powered electrode 514 without inducing plasma spikes, arcing,energy hot spots, or plasma instability.

[0132] In use and with continued reference to FIGS. 15-18, process gasenters the chamber lid 502 through the gas port 509 and is directedthrough gas passageways 513 to the upper side of gas distribution baffle546. Gas flows from the upper side of gas distribution baffle 546through gas outlets 517 into the plasma cavity 542, which promotesuniform process gas distribution in the plasma cavity 542. The RF energyapplied between the grounded plate 512 and the powered electrode 514ignites and sustains a plasma from the process gas residing in plasmacavity 542. The plasma in plasma cavity 542 is a full direct plasmacontaining ions, electrons, free radicals and molecular species. Becausethe flow of process gas in the plasma treatment system 10 is generallyconducted toward exhaust port 136 in bottom wall 44, the variouscomponents of the direct plasma in plasma cavity 542 will be attractedby a suction or vacuum force toward the slotted plates 516, 518, and 520that collectively constitute the grounded plate 512. Charged species,such as electrons and ions, recombine inside slots 522, 524, and 526because grounded plate 512 is grounded relative to earth ground. As aresult, ions and electrons are significantly less likely to enterprocessing space 102. The grounded plate 512 permits plasma specieslacking a net charge, such as free radicals and neutral molecules ofprocess gas, to be transported through slots 522, 524, and 526 into theprocessing space 102. The relative arrangement of slots 522, 524, and526 and the spatial relationship between the upper and center slottedplates 516, 518 and the center and lower slotted plates 518, 520eliminates, or substantially eliminates, line-of-sight paths from theplasma cavity 542 to the processing space 102 so that light generated bythe direct plasma in the plasma cavity 542 is not visible in processingspace 102.

[0133] The vacuum or the pumping action of vacuum pump 144 (FIG. 3)urges the free radicals and neutral molecules toward the workpiece 56 toperform the downstream-type plasma treatment. The workpiece 56 to betreated with the downstream-type plasma is supported by the side rails66 a, 66 b of substrate support 64. Free radicals admitted intoprocessing space 102 contact with the exposed surface 56 a of workpiece56 and react chemically with the material forming the workpiece 56 orcontamination covering the exposed surface 56 a to perform the surfacetreatment. Excess free radicals, unreactive process gas molecules, andcontaminants removed from the workpiece 56 are exhausted from theprocessing space 102 by the pumping action of vacuum pump 144.

[0134] While the present invention has been illustrated by a descriptionof various embodiments and while these embodiments have been describedin considerable detail, it is not the intention of the applicants torestrict or in any way limit the scope of the appended claims to suchdetail. Additional advantages and modifications will readily appear tothose skilled in the art. The invention in its broader aspects istherefore not limited to the specific details, representative apparatusand methods, and illustrative examples shown and described. Accordingly,departures may be made from such details without departing from thespirit or scope of applicants' general inventive concept. The scope ofthe invention itself should only be defined by the appended claims,

Wherein we claim:
 1. An apparatus for treating a workpiece with aplasma, comprising: a vacuum chamber including a processing space, achamber lid, and a plasma cavity defined in said chamber lid, saidplasma cavity and said processing space being in fluid communication; aworkpiece holder positioned in said processing space; a vacuum sourcecoupled in fluid communication with said vacuum chamber, said vacuumsource capable of evacuating said processing space and said plasmacavity; a process gas supply coupled in fluid communication with saidvacuum chamber, said process gas supply capable of providing process gasto at least said plasma cavity; and a first plasma excitation sourcecapable of exciting process gas in said plasma cavity to generate aplasma, said plasma excitation source including a grounded platepositioned between said plasma cavity and said processing space, saidgrounded plate having a plurality of openings capable of prohibiting thetransfer of ions and electrons from said plasma cavity to saidprocessing space and allowing the transfer of free radicals from saidplasma cavity to said processing space.
 2. The apparatus of claim 1,wherein said first plasma excitation source comprises a first poweredelectrode located in said plasma cavity, said first powered electrodecooperating with said grounded plate for generating the plasma in saidplasma cavity.
 3. The apparatus of claim 2, wherein said first plasmaexcitation source further comprises a first radio-frequency power supplyelectrically coupled with said first powered electrode, said firstradio-frequency power supply supplying radio-frequency excitation energyto said first powered electrode for exciting process gas in said plasmacavity.
 4. The apparatus of claim 3, further comprising a second poweredelectrode positioned in said processing space and a secondradio-frequency power supply electrically coupled with said secondpowered electrode, said second radio-frequency power supply capable ofproviding excitation energy to said second powered electrode forexciting process gas in said processing space to generate a plasma. 5.The apparatus of claim 4, wherein said first radio-frequency powersupply supplies radio-frequency power to said first powered electrodedriven 180° degrees out of phase relative to radio-frequency powersupplied to the second powered electrode by said second radio-frequencypower supply.
 6. The apparatus of claim 1, wherein said plurality ofopenings are arranged in a pattern corresponding to a geometrical shapeof the workpiece being plasma treated.
 7. The apparatus of claim 6,wherein an outer peripheral edge of said pattern correspondssubstantially to an outer peripheral rim of the workpiece.
 8. Theapparatus of claim 1, wherein said chamber lid is movable between openand closed positions for permitting introduction and removal of theworkpiece to and from said workpiece holder.
 9. The apparatus of claim8, further comprising: a loading station configured for introducing theworkpiece to said workpiece holder when said chamber lid is in the openposition; and an exit station configured for removing the workpiece fromsaid workpiece holder when said chamber lid is in the open position. 10.The apparatus of claim 1, wherein said chamber lid further includes aprocess gas inlet port coupling said process gas supply in fluidcommunication with said plasma cavity.
 11. The apparatus of claim 10,wherein said chamber lid further includes a gas distribution path fordistributing process gas received from said process gas inlet port tosaid plasma cavity.
 12. The apparatus of claim 11, wherein said firstplasma excitation source comprises a first powered electrode located insaid plasma cavity and an electrode insulator positioned between saidfirst powered electrode and said chamber lid, and said gas distributionpath includes a plurality of outlets proximate to said electrodeinsulator emitting process gas that seeps around an outer periphery ofsaid electrode insulator and an outer periphery of said first poweredelectrode for substantially uniform distribution into said plasmacavity.
 13. The apparatus of claim 11, wherein said gas distributionpath comprises a gas distribution baffle having a plurality ofspatially-arranged gas outlets positioned for distributing the flow ofprocess gas into said plasma cavity.
 14. The apparatus of claim 1,wherein said grounded plate is removably positioned between said plasmacavity and said processing space.
 15. The apparatus of claim 1, whereinsaid openings are arranged to substantially eliminate line-of-sightpaths between said processing space and said plasma cavity.
 16. Theapparatus of claim 15, wherein said grounded plate comprises a pluralityof slotted plates each having a slot arrangement that cooperates forsubstantially eliminating line-of-sight paths.
 17. The apparatus ofclaim 16, wherein adjacent ones of said slotted plates have inter-plateseparations in a direction extending between said plasma cavity and saidprocessing space that cooperate with said slot arrangement forsubstantially eliminating line-of-sight paths.
 18. The apparatus ofclaim 16, wherein said slot arrangement of at least one of said slottedplates is offset spatially from said slot arrangement of at leastanother of said slotted plates.
 19. The apparatus of claim 18, whereinsaid vacuum chamber has a machine direction in which workpieces aretransported, and said slot arrangement in said at least one slottedplate is offset parallel to the machine direction.
 20. The apparatus ofclaim 1 wherein said plasma cavity is defined by a plurality ofinwardly-oriented surfaces of said chamber lid and a surface of saidgrounded plate, said powered electrode being positioned equidistantlyfrom said plurality inwardly-oriented surfaces of said chamber lid andsaid surface of said grounded plate.
 21. An apparatus for treating aworkpiece with plasma, comprising: a vacuum chamber having a chamberbase and a chamber lid movable relative to said chamber base between aclosed position that defines a processing space and an open position fortransferring a workpiece into and out of said processing space, saidchamber lid including a first sidewall section capable of being removedfrom said chamber lid for changing a vertical dimension of said vacuumchamber; a vacuum source coupled in fluid communication with said vacuumchamber, said vacuum source capable of evacuating said processing space;a workpiece holder located in said processing space; a process gassupply in fluid communication with said vacuum chamber, said gas supplycapable of providing process gas to said processing space; and a plasmaexcitation source operable to provide a plasma in said processing spacegenerated from said process gas.
 22. The apparatus of claim 21, whereinsaid chamber lid further comprises a domed ceiling section including aplasma cavity, and said plasma excitation source includes a poweredelectrode positioned in said plasma cavity.
 23. The apparatus of claim22, wherein said plasma excitation source further comprises a groundedplate positioned between said plasma cavity and said processing space.24. The apparatus of claim 23, wherein said grounded plate includes aplurality of openings capable of preferentially transferring freeradicals from a plasma in said plasma cavity to said processing space.25. The apparatus of claim 22, further comprising a second sidewallsection capable of sealingly engagement with said chamber base, saidfirst sidewall section being positioned between said domed ceilingsection and said second sidewall section.
 26. The apparatus of claim 25,further comprising a guide for aligning said first sidewall section withsaid second sidewall section.
 27. The apparatus of claim 26, whereinsaid guide is further capable of aligning said second sidewall sectionwith said domed ceiling section.
 28. The apparatus of claim 25, furthercomprising a guide for aligning said removable sidewall section withsaid domed ceiling section.
 29. The apparatus of claim 21, wherein saidplasma excitation source comprises a powered electrode that is part ofan assembly which includes said workpiece holder.
 30. A method of plasmatreating a workpiece having a thickness and an exposed surface in aprocessing space of a vacuum chamber having a chamber lid and atreatment electrode positioned in the chamber lid, comprising: varying avolume of the chamber lid to alter the distance from the exposed surfaceof the workpiece to the treatment electrode based upon the thickness ofthe workpiece; placing a workpiece in the processing space; and exposingthe exposed surface of the workpiece to the plasma.
 31. The method ofclaim 30, wherein the varying of the volume further comprises removingat least one sidewall section from the chamber lid.
 32. The method ofclaim 30, wherein the varying of the volume further comprises adding atleast one sidewall section to the chamber lid.
 33. A method of treatinga workpiece with a plasma, comprising: placing the workpiece in aprocessing space of a plasma processing system; generating a directplasma comprising charged species and free radicals from a process gas;filtering charged species from the direct plasma to create adownstream-type plasma including free radicals; and exposing theworkpiece in the processing space to the free radicals in thedownstream-type plasma.
 34. The method of claim 33, wherein thefiltering of the charged species includes positioning a groundedperforated plate between a plasma cavity in which the direct plasma isgenerated and the processing space, the perforations being capable ofpreferentially transferring free radicals from the direct plasma in theplasma cavity to the processing space.
 35. The method of claim 34,wherein the plasma processing system includes a vacuum chamber with amovable chamber lid and a plasma cavity in the chamber lid separatedfrom the processing space by the grounded perforated plate, and whereinthe generating of the direct plasma occurs in said plasma cavity. 36.The method of claim 33, wherein said process gas is air, said directplasma is generated from air, and said second plasma contains radicalscharacteristic of constituent gases in air.
 37. The method of claim 33,wherein the generating of the direct plasma produces light, and furthercomprising substantially eliminating the transfer of light originatingfrom the direct plasma into the processing space.